/*
 * Copyright (C) 2007 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;

/**
 * Implementation of {@link Multimap} using hash tables.
 * 
 * <p>
 * The multimap does not store duplicate key-value pairs. Adding a new key-value
 * pair equal to an existing key-value pair has no effect.
 * 
 * <p>
 * Keys and values may be null. All optional multimap methods are supported, and
 * all returned views are modifiable.
 * 
 * <p>
 * This class is not threadsafe when any concurrent operations update the
 * multimap. Concurrent read operations will work correctly. To allow concurrent
 * update operations, wrap your multimap with a call to
 * {@link Multimaps#synchronizedSetMultimap}.
 * 
 * @author Jared Levy
 * @since 2010.01.04 <b>stable</b> (imported from Google Collections Library)
 */
@GwtCompatible(serializable = true)
public final class HashMultimap<K, V> extends AbstractSetMultimap<K, V> {
    private static final int DEFAULT_VALUES_PER_KEY = 8;

    @VisibleForTesting
    transient int expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;

    /**
     * Creates a new, empty {@code HashMultimap} with the default initial
     * capacities.
     */
    public static <K, V> HashMultimap<K, V> create() {
        return new HashMultimap<K, V>();
    }

    /**
     * Constructs an empty {@code HashMultimap} with enough capacity to hold the
     * specified numbers of keys and values without rehashing.
     * 
     * @param expectedKeys
     *            the expected number of distinct keys
     * @param expectedValuesPerKey
     *            the expected average number of values per key
     * @throws IllegalArgumentException
     *             if {@code expectedKeys} or {@code expectedValuesPerKey} is
     *             negative
     */
    public static <K, V> HashMultimap<K, V> create(int expectedKeys,
            int expectedValuesPerKey) {
        return new HashMultimap<K, V>(expectedKeys, expectedValuesPerKey);
    }

    /**
     * Constructs a {@code HashMultimap} with the same mappings as the specified
     * multimap. If a key-value mapping appears multiple times in the input
     * multimap, it only appears once in the constructed multimap.
     * 
     * @param multimap
     *            the multimap whose contents are copied to this multimap
     */
    public static <K, V> HashMultimap<K, V> create(
            Multimap<? extends K, ? extends V> multimap) {
        return new HashMultimap<K, V>(multimap);
    }

    private HashMultimap() {
        super(new HashMap<K, Collection<V>>());
    }

    private HashMultimap(int expectedKeys, int expectedValuesPerKey) {
        super(Maps.<K, Collection<V>> newHashMapWithExpectedSize(expectedKeys));
        Preconditions.checkArgument(expectedValuesPerKey >= 0);
        this.expectedValuesPerKey = expectedValuesPerKey;
    }

    private HashMultimap(Multimap<? extends K, ? extends V> multimap) {
        super(Maps.<K, Collection<V>> newHashMapWithExpectedSize(multimap
                .keySet().size()));
        putAll(multimap);
    }

    /**
     * {@inheritDoc}
     * 
     * <p>
     * Creates an empty {@code HashSet} for a collection of values for one key.
     * 
     * @return a new {@code HashSet} containing a collection of values for one
     *         key
     */
    @Override
    Set<V> createCollection() {
        return Sets.<V> newHashSetWithExpectedSize(expectedValuesPerKey);
    }

    /**
     * @serialData expectedValuesPerKey, number of distinct keys, and then for
     *             each distinct key: the key, number of values for that key,
     *             and the key's values
     */
    private void writeObject(ObjectOutputStream stream) throws IOException {
        stream.defaultWriteObject();
        stream.writeInt(expectedValuesPerKey);
        Serialization.writeMultimap(this, stream);
    }

    private void readObject(ObjectInputStream stream) throws IOException,
            ClassNotFoundException {
        stream.defaultReadObject();
        expectedValuesPerKey = stream.readInt();
        int distinctKeys = Serialization.readCount(stream);
        Map<K, Collection<V>> map = Maps
                .newHashMapWithExpectedSize(distinctKeys);
        setMap(map);
        Serialization.populateMultimap(this, stream, distinctKeys);
    }

    private static final long serialVersionUID = 0;
}
